This invention is related to a mechanical vibrating drive system for a vibratory conveyor apparatus and, more particularly, to a vibratory conveyor apparatus utilizing the natural frequencies of two spring sets to impart a resultant vibratory drive force to the conveyor apparatus.
There are various vibrating drive systems for controlling the direction and/or speed of product being carried by a vibratory conveyor. The vibrating conveyor apparatus typically includes a trough mounted for vibratory motion, such as provided by a plurality of springs. In general, product is moved along the conveyor trough by a force applied to the trough. The product can be moved along a linear path or along an elliptical path, the path being determined by the force applied to the conveyor trough.
One type of vibrating drive system is a mechanical system utilizing fixed eccentric rotating weights and a phase angle adjustment means. A system of this type is described in detail in U.S. Pat. No. 5,064,053, assigned to the same assignee as the present invention. In the system of the '053 patent, a single rotating shaft bearing an eccentric weight is in a parallel relationship with and positioned between paired additional rotating shafts bearing eccentric weights. The centered single shaft rotates in one direction while the paired shafts rotate in the opposite direction but at the same number of revolutions per minute. When the shafts rotate, the weights impart a force to the conveyor trough which, in turn, causes the product to move along the conveyor. Because the force to move the product is supplied by the eccentric weights, the force generated in insensitive to the product load on the conveyor. Thus, there is a consistent force generated by the drive system regardless of the type or quantity of product that is conveyed. The user can reverse the direction in which the material is being conveyed, but to ensure that product moves along the desired path requires physically changing the positioning of one or more of the eccentric weights and its associated shaft by repositioning the phase angle adjustment means. This change-over requires considerable down time, which is highly undesirable when time is a critical factor in the application.
A second type of vibrating drive system is a mechanical system that uses a reversible motor and dynamic balancers to produce the driving forces. A system of this type is described in U.S. Pat. No. 5,713,457, assigned to General Kinematics Corporation. In the system of the '457 patent, a reversible motor with a rotary output shaft and eccentric weight is mounted near the center of gravity on a conveyor apparatus, and a dynamic balancer is positioned at each end of the conveyor trough. The dynamic balancers are spring and weight systems designed to move the product in an elliptical path as it travels along the conveyor trough. For optimum performance, the dynamic balancers (or absorbers) must be selected such that their natural frequency is just greater than the operational frequency of the system as determined by the frequency of the motor. Maintaining a consistent driving force can be difficult with this type of system because the dynamic balancers are very highly tuned, so small changes in product load or motor speed may affect the performance of the equipment. In particular, the user must be cautious of producing overstrokes that can permanently damage the conveying equipment. As with the eccentric weight systems, the user can reverse the direction of product flow in the system of the '457 patent by reversing the motor. However, because the dynamic balancers are set only for one speed, to make any changes in the system other than reversing the direction of product flow requires that the system be completely modified, which can result in considerable down time.
Eccentric weight systems that include electronic drive capabilities, such as described in U.S. Pat. No. 5,615,763, assigned to the same assignee as the present invention, allow for a rapid change of direction of the product flow. However, such systems are expensive relative to the cost of mechanical systems.
Thus, there is a paramount need for an inexpensive mechanical vibrating drive system that will allow the user to easily and frequently change the direction of flow of the conveyed product without incurring the down time of the system heretofore necessary with prior art mechanical vibrating drive systems. In addition, there is a need for an inexpensive conveying system that will allow the user to convey product along a reversible, symmetric, elliptical path as it travels along the conveyor trough. Further, there is a need for a natural frequency conveyor that will allow product to be conveyed long distances as compared to the prior art feeders which arc limited in length, and for a natural frequency conveyor that preferably will incur relatively low maintenance costs for the user.